Device performance and wavelength tuning behavior of ultra-short quantum-cascade microlasers with deeply etched Bragg-mirrors

The fabrication and charactersitics of edge-emitting quantum-cascade (QC) lasers and microlasers with monolithically integrated deeply etched semiconductor-air Bragg-mirrors based on GaAs is reported. We observe a reduction of the threshold current density by 25% and an increase of the operation temperature by 23 K to a maximum of 315 K for 800 mu m long devices by employing Bragg-mirrors. Devices with ultra-short cavities of about 100 mu m (similar to 40 times the wavelength) operate up to 260 K. At 80 K, these devices show threshold currents as low as 0.63 A and output levels up to 56 mW. In these devices, longitudinal single mode operation with output levels exceeding 7.7, 5.6, and 2.8 mW was measured at 180, 200, and 240 K, respectively. This can be attributed to the limited gain bandwidth of QC lasers and the large mode spacing in these devices. By temperature control the emission wavelength can be tuned without mode jumps over 80 mu. The feasibility to pre-select the emission wavelength by a direct control of the Fabry-Perot mode was demonstrated by microlasers with 1 mu m cavity length difference.